The present invention relates generally to the communication of data in a packet communication system, such as a WLAN (Wireless Local Area Network), constructed pursuant to the IEEE 802.11 standard. More particularly, the present invention relates to a manner by which to communicate variably-sized data packets pursuant to a SDMA (Space-Division, Multiple-Access) scheme. Communication capacity of the packet communication system is significantly increased through operation of an embodiment of the present invention as communications pursuant to more than one communication session are simultaneously effectuable.
A communication system is formed, at a minimum, of a transmitting station and a receiving station interconnected by a communication channel. Communication signals generated by the transmitting station are transmitted upon the communication channel to be received by the receiving station.
A radio communication system is a communication system in which at least a portion of the communication channel is formed of a portion of the electromagnetic spectrum. Increased mobility of communications is permitted as a fixed or hard-wired connection is not required to be formed between the transmitting and receiving stations.
A cellular communication system is an exemplary radio communication system. A subscriber to a cellular communication system, when positioned at almost any location throughout an area encompassed by the network infrastructure of the cellular communication system, is able to communicate by way of the system with a mobile terminal.
The network infrastructure of an exemplary cellular communication system includes spaced-apart, fixed-site base stations which include transceivers. In such an exemplary system, each fixed-site base station defines a cell. As the mobile terminal used by the subscriber to communicate with another communication station travels between cells of the system, uninterrupted communication is possible by handing-over communications from one base station to another.
Several analogous types of wireless communication systems have been implemented, and others have been proposed, to encompass limited areas, such as the area encompassed by a building structure or office workplace. Wireless communication systems sometimes referred to as microcellular networks, private networks, and WLANs (Wireless Local Area Network) are exemplary of such systems.
Wireless communication systems are typically constructed pursuant to standards promulgated by a regulatory or quasi-regulatory body. For instance, the IEEE 802.11 standard, and variants thereof, promulgated by the IEEE (Institute of Electrical and Electronic Engineering) is a wireless LAN standard pertaining generally to communications at various wireless frequencies including a 5 GHz range and a 2.4 GHz range. The 802.11 standard specifies an over-the-air interface between a wireless client, e.g, a mobile terminal, and a base station or access point, as well as among wireless clients. Standards pertaining to a physical layer and a MAC (Media Access Control) layer are set forth in such standard. The standard permits automatic medium sharing between different devices which includes compatible physical layers. Asynchronous data transfer is provided for in the standard, generally by way of the MAC layer which utilizes a CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) communication scheme.
The IEEE 802.11 standard provides for a Time-Division Duplexing (TDD) having Carrier-Sense, Multiple-Access and Collision Avoidance (CSMA/CA). Proposals have been set forth to also provide for SDMA (Space-Division, Multiple-Access) communications in the existing scheme.
By providing for a SDMA communication scheme, the communication capacity of the WLAN would be significantly increased. Analogously, in other communication systems, providing for SDMA communications would similarly also significantly increase the communication capacity of such a communication system.
The communication scheme defined in the IEEE 802.11 standard, however, provides for packet communications in which packet sizes are variably sized, depending, for instance, upon the amount of data to be communicated pursuant to a communication session. The communication scheme also provides for a receiving station which receives data packets to acknowledge their receipt.
When only a single communication session is effectuated within a single time slot of the TDD scheme, a conventional packet data send-acknowledgment scheme works without difficulty. However, when two or more data packets are communicated simultaneously during a single time slot of the TDD scheme, detection of multiple acknowledgments, indicating successful transmission of data packets pursuant to more than one communication session, become problematical. A sending station, e.g., sending data packets pursuant to two or more communication sessions simultaneously, is unable to detect an acknowledgment returned by a receiving station pursuant to one communication session if the sending station is still sending data pursuant to another communication session. Because of the potentially unequal sizes of the data packets to be communicated pursuant to the separate communication sessions, acknowledgments are likely unable to be detected as required pursuant to the communication scheme.
A manner by which to ensure that the acknowledgments to acknowledge reception of data packets communicated pursuant to separate communication sessions is necessary to permit proper operation of a packet data communication system. If a manner could be provided by which to ensure that the acknowledgments are successfully received, use of SDMA in a packet communication system, such as a WLAN operable pursuant to the IEEE 802.11 standard, would be workable.
It is in light of this background information related to packet communication systems that the significant improvements of the present invention have evolved.
The present invention, accordingly, advantageously provides apparatus, and an associated method, by which to communicate data in a packet communication system, such as a WLAN (Wireless Local Area Network), constructed pursuant to the IEEE 802.11 standard.
Through operation of an embodiment of the present invention, variably-sized data packets are communicated pursuant to a SDMA (Space-Division, Multiple-Access) scheme. By providing a workable SDMA scheme, the communication capacity of the packet communication system is significantly increased as communications pursuant to more than one communication session are simultaneously effectuable.
In one aspect of the present invention, determination is made of the lengths of the data packets to be communicated pursuant to separate communication sessions which are to be effectuated during a common time period, such as a time slot, in the SDMA communication scheme. The determination is at least a relative determination of the relative lengths of the data to be communicated pursuant to the separate communication sessions. Data which is of a lesser length than a longest-length data transmission is thereby determined. Responsive to such determination, such data is padded with additional data so that the data lengths of the data to be communicated pursuant to the separate communication sessions are all of the same length. The padded data, in one implementation, is merely dummy data, not to be utilized by the receiving station which receives the data. In another implementation, the padded data includes, or pertains to, error correcting code which is used for error correction purposes. By sending data all of the same lengths, the sending station, such as an access point in a WLAN, is thereby able to complete transmission of the data, or a portion thereof, and thereafter detect acknowledgments generated responsive thereto. Because transmission of the data pursuant to the separate communication sessions ends at substantially the same time, the possibility that an acknowledgment shall fail to be detected is reduced.
In another implementation, xe2x80x9cnull paddingxe2x80x9d is utilized, and operation is analogous to a delayed-ACK scheme. In a delayed-ACK scheme, the recipient of a data packet is commanded to wait for a specified time period, subsequent to reception of the pocket, and prior to the transmission of an ACK indication.
In contrast to dummy-data padding, null padding reduces intra-SDMA interference. In downlink SDMA communications, the transmit power is focused on the not-padded portion of the burst. Essential for null-padded SDMA operation is how a mobile terminal reacts to the vanishing of the received signal strength during the padded portion. The length of a packet can also be tuned with modulation such that selecting a lower-datarate modulation results in a longer packet and vice versa. This can help to reduce the amount of padding if a lower-datarate modulation is selected for the shorter of the simultaneously transmitted packets.
In another aspect of the present invention, in addition to padding of one or more data sequences to be communicated pursuant to a communication session, the data to be communicated pursuant to the separate communication sessions is divided into data fragments. First data fragments are communicated pursuant to the separate communication sessions for a selected time period. The data fragments are all of substantially the same length when transmission of the fragments is completed, transmission ends for a period to permit the receiving stations to acknowledge reception of the data fragments. Thereafter, additional data fragments are communicated in like manner. By dividing data into data fragments, lesser amounts of padding need to be applied to data streams other than the longest of the data streams. Additional overhead is introduced, however, as additional acknowledgments, and their corresponding overhead, are generated.
In another aspect of the present invention, a manner is provided by which to dynamically fragment the data communicated pursuant to the separate communication sessions. In one implementation, a fragment length is initially selected to be of a defined length. Subsequent fragment lengths are determined according a shortest remaining amount of data to be communicated pursuant to one of the communication sessions. Thereby, padding of data on one or more of the data streams is not required. However, again, by defining fragments to be of short durations, increased overhead due to the acknowledgments, and their associated overhead, is required.
In one implementation, a manner is provided by which to permit SDMA (Space-Division, Multiple-Access) operation of a WLAN operable pursuant to the IEEE 802.11 standard. Determinations are made of data sizes of data to be communicated pursuant to more than one communication session upon a single channel, such as a single time slot of a TDD (Time Division Duplex) scheme. Responsive to the determinations, the data communicated pursuant to each of the communication sessions is caused to end, at least for selected time periods, at common time periods. Subsequent to the ending of the data communication, acknowledgments are returned to the sending station. Thereby, the sending station is able to detect the acknowledgments acknowledging receipt at respective receiving stations of the data communicated pursuant to the separate communication sessions. The data communicated pursuant to the separate communication sessions are caused to be of equal lengths either by adding, i.e., padding, data to one or more of thedata streams or by defining data fragments into which the data streams are divided.
In these and other aspects, therefore, apparatus, and an associatedmethod, is provided for a multi-user, packet communication system. The system at least permits packet data of selected data sizes to be communicated by a network communication station to a first remote station pursuant to a first communication session. And, packet data of selected data sizes is further permitted to be communicated by the network communication station to at least a second remote communication station pursuant to at least a second communication session. Concurrent communications during a selected time period pursuant to the first and the at least second communication sessions is facilitated. A determiner is coupled to receive indications of the selected data sizes of the data to be communicated during the first and at least second communication sessions. The determiner determines at least relative sizes of the data to be communicated pursuant to each of the first and at least second communication sessions. A packet data transmitter is operable to transmit concurrently and for a selected time period data pursuant to the first communication session and data pursuant to the second communication session. The selected time period is selected responsive to determinations made by the determiner.